Irrigation systems are used to provide water to a wide variety of devices, including, for example, spray nozzles, sprinkler heads, and drip hoses. Such systems generally make use of control valves to command the flow of water under pressure through the system. The control valve generally comprises a valve housing having an inlet for connection to a source of water under pressure, and an outlet for connection via suitable conduits to associated watering devices. A valve member is mounted within the valve housing for movement between open and closed positions relative to a valve seat for controlled coupling of the water supply to the watering devices. In one common form, the water supply valve may include a remotely operated solenoid actuator for displacing the valve member between the open and closed positions. In addition, the supply valve regulates the flow rate such as with a pressure responsive resilient diaphragm for movably positioning the valve member in a manner to maintain a substantially constant flow rate so long as the pressure of the supply water is above a predetermined threshold.
In common water supply valves, the valve housing is constructed from two or more housing components formed from cast metal or molded plastic, and assembled with the associated valve member and resilient diaphragm movably mounted therein. In a jar top valve, the two main housing components are a base, comprising an inlet and an outlet, and a bonnet which is threaded onto the base and which defines, with the base, a pressure chamber.
In a reverse flow diaphragm valve, fluid enters the housing through an inlet and flows into a pressure chamber. A valve member is carried by a resilient diaphragm and is located within the pressure chamber and divides the pressure chamber into an inlet chamber and a control chamber. An annular valve seat is located at the downstream end of the inlet chamber. The valve member can be in a closed position, sealing against the valve seat and shutting off flow through the valve, or in a range of open positions, permitting and possibly regulating flow through the valve to an outlet.
The valve may be closed manually by driving the valve member against the valve seat using a control piston and spring. Alternatively, a solenoid actuator can be used to control the opening and closing of the valve by manipulating the hydraulic forces acting on the diaphragm. When the solenoid actuator is in its open position, it vents the control chamber through a feed port to relieve pressure therein. Hydraulic forces on the diaphragm come into equilibrium and the diaphragm allows movement of the valve member from the closed position to a range of open positions permitting controlled flow through the valve. When the solenoid actuator is in its closed position, the feed port is sealed and fluid pressure builds up in the control chamber, acting to urge the diaphragm and valve member to the closed position prohibiting flow through the valve assembly.
Flow through the valve is controlled by the position of a control piston which can be manipulated by hand via a flow control handle. The position of the control piston determines position of a spring used to apply a biasing force to the valve member. As the control piston is lowered, the biasing force of the spring increases and the valve member is urged closer to the valve seat, leading to a greater pressure drop across the valve and reducing the flow rate through the valve. The pressure drop across the valve is reflected in a corresponding pressure differential between the inlet chamber and the control chamber. Under low flow conditions, this pressure differential across diaphragm, and the displacement of the diaphragm, are greatest. This can create stresses on resilient diaphragm member and can lead to tearing and generally reduced life of the diaphragm material. Accordingly, there is a need for an improved diaphragm valve that can protect the resilient diaphragm from undue stresses and prolong its life.